best DIY "gotta have" for a WDW trip? Something you made yourself to get around inconvenience or high costs; such as freezing juice boxes/pouches to keep your sandwiches cold in their cooler... Eat your heart out, MacGyver.
Mine is the autograph books that I made for my kids. I got tired of spending outrageous prices in the parks just to have something Disney-themed, and hit on the idea of buying a few sheets of heavy weight paper, a couple sheets of sturdy cardstock, some stickers and glittery bits in Disney themes--all for under 15 dollars at my local craft shop. Then off to Staples office supply, where they happily measured, cut and spiral-bound my miniature books into autograph size. Kiddos decorated 'em with the stickers to make a personalized book that nobody else will have, and each page is big enough for a costumed CM to grab and hold with those cumbersome mitts in order to sign. There's even enough room for a character photo on the facing pages. I'm turrible proud of 'em...and I spent less than I would have on the standard issue ones at the parks!